CTCP AVATAR

Opening a pull request just to track changes.

Description of the solution:

When nick N1 from host H1 sends a message and host H1 does not exist in "convos:host2convos" it will do a ```CTCP AVATAR``` request to nick N1. If N1 responds with a ```CTCP AVATAR NOTICE```, the host will be stored in "convos:host2convos", so the next time a user from H1 sends a message, the avatar is fetched from the Convos instance running on H1. (Note: The ```NOTICE``` actually contains the URL to the Convos instance, since it may very well not be H1)

This means that the first message will NOT have the correct avatar. We could probably fix this using a timer and watch "convos:host2convos" to see if it gets populated before a given timeout, but I'm not sure if it's worth it, compared to the complexity required.